The present invention relates generally to the field of test methods and systems. More specifically, the present invention relates generally to a method and system for in situ testing of the performance characteristics of fiber optic cable assemblies and components.
Prior to the present invention, isolation of failures in fiber optic systems, such as those found aboard aircraft, have been impossible without complete removal of fiber optic cables, fiber optic connectors, and other components. Thus, in light emitting diode ("LED") based fiber optic transmission systems, for example, the effect of reflections due to fiber optic connectors are often ignored. Similar to electrical transmission systems, reflections in fiber optical transmission systems distort the transmitted signals and impair the system's ability to transfer information. The level of impairment depends on the amplitude of the reflections, the delay between reflections, and the attenuation in the transmission media between reflection sources. Attenuation in a transmission path reduces the amplitude of reflections and thus their effect. Therefore, reflections in a fiber optic transmission system have a more significant impact on system performance because of the extremely small amount of attenuation (e.g., on the order of 0.5-dB per kilometer) in transmission paths between connectors.
In military avionics applications, a typical fiber optic transmission path contains many connections. These connections typically occur in mass terminated connectors (e.g., MIL-C-38999 insert connectors) which contain many other types of connections, such as wires of different sizes and coaxial connections. The poor performance of these types of fiber optic connectors severely impairs the performance of fiber optic transmission systems. Historically, connectors have been a source of intermittent system failures. Because, prior to the present invention, there was no method of measuring a connector's performance level or isolating link problems to a particular connector in multiple connector systems, periodic maintenance is performed on every connector in an aircraft.
A maintenance action includes disconnecting a connection, cleaning the ends of the fiber with a solvent, and reconnecting the fiber. Aside from injecting cost into the picture, these maintenance actions were often ineffective or created connections with poor performance.